1. Field of the Invention
The present invention relates to a method for fabricating micro-electro-mechanical structure, and more particularly to a method for fabricating a microstructure, which can effectively avoid improper erosion, reduce the probability of exposure of the microstructure and further reduce the package cost.
2. Description of the Prior Art
The existing semiconductor micro-electro-mechanical systems comprises various semiconductor microstructures, such as the unmovable probe, channel, cavity structure, or the movable spring, linkage rod, gear (rigid body movement or flexible deformation), etc.
Integrating the above different structures with the related semiconductor circuit can form various semiconductor applications. Thus, how to utilize the fabricating method to improve the various functions of the microstructure is the key index of the semiconductor electromechanical system in the future and is also a rigorous challenge of further developing the chip in the future.
The existing method for fabricating the micro-electro-mechanical sensor and actuator system is often required to fabricate a suspension structure on a silicon substrate. The above process must adopt the advanced semiconductor technology, such as: high-aspect-ratio dry etching and sacrificial layer removing technology, etc.
A first conventional method disclosed in U.S. Pat. No. 6,458,615 B1 is to form at least one insulation layer including an inner micro-electro-mechanical structure on an upper surface of a silicon substrate, and then conduct a layer-by-layer etching operation from the upper surface until the lateral edge of the micro-electro-mechanical structure, and finally, conduct an isotropic dry etching to the silicon substrate to achieve the suspension of the micro-electro-mechanical structure;
The first conventional method can be used to fabricate a suspension micro-electro-mechanical structure, but it has the following disadvantages:
1. It adopts anisotropic dry chemical etching and uses chemical reaction to remove the isolation layer, however, after the side edge of the micro-electro-mechanical structure is etched, the silicon substrate still needs to be massively etched by isotropic chemical etching, and this technique will produce serious undercut problems;
2. In the process of this conventional technology, the micro-electro-mechanical structure is exposed in the process at first, after a long time of multi-layer processing, the exposed micro-electro-mechanical structure is likely to be contaminated and damaged, causing an excessively low yield rate;
3. After the etching operation is completed, the micro-electro-mechanical structure has already been capable of operating in suspension state, but a special machine will be used to pack the micro-electro-mechanical structure surface to block dust and particle. However, since the micro-electro-mechanical structure must be ensured in the suspension state, the conventional method is to place a special mold used as a cap over the product surface, and then precisely fabricate a package protection cap without touching the suspension micro-electro-mechanical structure. This kind of surface package is complicated and expensive, and unlikely to be integrated with the process of the common integrated circuit package.
With the rapid development of the above technology, in order to improve many problems, a second conventional method disclosed in U.S. Pat. No. 6,712,983 B2 taught the use of a reactive ion etch (hereinafter refereed to as RIE) technology. This technology is capable of greatly reducing occurrence of the undercut, but since it also conducts a layer-by-layer etching from up down, and the last etching operation of the silicon substrate must apply the isotropic etching technology, this improved conventional technology is still complicated and has the undercut problem, and some problems still have not been improved, such as the exposure of the micro-electro-mechanical structure and being not good for later package.
It is to be noted that, in the conventional top-down etching technology, the respective structures in the microstructure and the metal layer are stacked layer by layer. When fabricating a complicated multi-layer suspension microstructure, the multi-layer suspension microstructure must ensure not to be affected by multiple etching operations, and not to be damaged after being etched and exposed for a long time, and further ensure to avoid the fine structure remains of multiple etching operations.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.